1. Field of the Invention
The invention relates generally to compositions for golf balls. More specifically, the invention relates to fillers for golf ball centers and cores.
2. Description of the Related Art
One of the parameters of golf ball performance that receives great attention is flight distance. Although there are a variety of factors that influence a golf ball's flight distance, perhaps the most important factor relates to the rebound characteristics of the ball which is dictated in large part by the materials used to construct the golf ball.
As is well known in the industry, there are a number of different types of golf balls. The predominant varieties are a two-piece and a three-piece golf ball. A two piece golf ball is typically constructed with a solid core and a cover. A three-piece ball is typically a thread wound solid center with a cover. Within these two broad categories are numerous variations such a liquid filled centers for three-piece balls. Regardless of the particular golf ball type, all golf balls have rebound characteristics that are dictated by the materials and construction type utilized.
To conform to United States Golf Association ("U.S.G.A.") guidelines and regulations, golf balls have to be constructed to meet specific weight requirements. When a golf ball core or center composition is below specified weight requirements, one of the techniques used to increase weight is to add fillers to the centers and cores of three-piece golf balls and two-piece golf balls, respectively. Conventional fillers used include calcium carbonate (specific gravity of 2.73), barium sulfate (sp. gr. of 4.3) and zinc oxide (sp. gr. 5.6). Although these materials can be effectively used to increase the weight of a golf ball, the inevitable volume occupied by these materials when incorporated into a center or core results in a reduction in the polymer/rubber content of the center or core. By extending the rubber with fillers or reducing the polymer/rubber content, the coefficient of restitution of the resulting golf ball is reduced which translates into reduced flight distance.
The compression of a golf ball is a measure of the deflection of the golf ball under a load of 200 lbs. The Professional Golf Association (PGA) measures compression as (0.180"-deflection).times.100. Typically, the lower the PGA compression the softer the golf ball. The softer golf ball (with a softer core and/or cover) exhibits better feel, click and spin characteristics when compared with a high compression golf ball.
An additional detrimental side effect of high stiffness content is that a high loading of fillers stiffens the rubber compound and increases the compression of the core or center while reducing the resilience properties.
It has now been discovered that the incorporation of high density materials such as tungsten into cores and centers can be used to meet golf ball weight requirements without significantly reducing the coefficient of restitution or increasing the compression of the golf ball produced. In some instances, the opposite effect has been observed.
It is thus an object of the invention to provide a golf ball center or core composition that uses high specific gravity fillers in order to maintain the weight of a conventional golf ball core or center having a lower compression without significantly compromising the resilience characteristics of the golf ball in which such a center or core is incorporated. A further object is to meet the USGA golf ball weight requirements without increasing the golf ball compression.